The offspring of an extremely advanced prehistoric races who built cavern cities inside the Earth before abandoning Earth for another planet due to damaging radiation from the Sun. The dero have degenerated over time into a population of mentally impaired sadists.

These Deros still lived in the cave cities, spying upon the Underdwellers, the remnants of Humanity, and the Apes. They have access to sophisticated "ray" machinery that the great ancient races had left behind.